to the eye. Take, for example, the very
chromatic pigments representing red and green, such as vermilion and
emerald green. If each emitted a single pure hue free from trace of any
other hue, then their mixture would appear yellow, as when spectral red
and green unite. But, instead of yellow, their mixture produces a warm
gray, called brown or "dull salmon," and this is to be inferred from
their spectra, where it is seen that vermilion emits some green and
purple as well as its dominant color, while the green also sends some
blue and red light to the eye.[20]

[Footnote 20: See Rood, Chapter VII., on Color by Absorption.]

Thus stray hues from other parts of the spectrum tend to neutralize the
yellow sensation, which would be strong if each of the pigments were
pure in the spectral sense. Pigment absorption affects all palette
mixtures, and, failing to obtain a satisfactory yellow by mixture of red
and green, painters use original yellow pigments,--such as aureolin,
cadmium, and lead chromate,--each of them also impure but giving a
dominant sensation of yellow. Did the eye discriminate, as does the ear
when it analyzes the separate tones of a chord, then we should recognize
that yellow pigments emit both red and green rays.

White light dispersed into a colored band by one prism, may have the
process reversed by a second prism, so that the eye sees again only
white light. But this would not be so, did not the balance of red,
green, and violet-blue sensations remain undisturbed. All our ideas of
color harmony are based upon this fundamental relation, and, if pigments
are to render harmonious effects, we must learn to control their
impurities so as to preserve a balance of red, green, and violet-blue.

Otherwise, the excessive chroma and value of red and yellow pigments so
overwhelm the lesser degrees of green and blue pigments that no balance
is possible, and the colorist of fine perception must reject not alone
the theoretical, but also the practical outcome of a "red-yellow-blue"
theory.

Some of the points raised in this discussion are rather subtle for
students, and may well be left until they arise in a study of optics,
but the teacher should grasp them clearly, so as not to be led into
false statements about primary and complementary hues.

CHAPTER IV.

PRISMATIC COLOR.

+Pure color is seen in the spectrum of sunlight.+

(87) The strongest sensation of color is gained in a darkened room, with